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ASP.NET Core–Health checks

ASP.NET Core offers Health Checks Middleware for reporting the health of your application. Health checks are exposed as HTTP endpoints and can be probed by container orchestrators and load balancers to check an app's status.

For Kubernetes I typically create 2 type of health checks:

  • Readiness indicates if the app is running normally but isn't ready to receive requests.
  • Liveness indicates if an app has crashed and must be restarted.

This is a general guideline we use for all containerized applications that we have running in Kubernetes.

Last week I was reviewing one of those applications and I noticed the following code:

This code is perfectly fine, but I couldn’t remember exactly what the role of the Predicate was in the example above. Time to dig in somewhat deeper…

By default, the Health Checks Middleware runs all registered health checks. To run a subset of health checks, you can provide a function that returns a boolean to the Predicate option.

So in the example above, the readiness check will only run healthchecks tagged with ‘ready’. The second health check, the liveness check, will run none of the available health checks.

To tag a specific healthcheck, you should configure this when adding the healthcheck:

More information: https://docs.microsoft.com/en-us/aspnet/core/host-and-deploy/health-checks?WT.mc_id=DOP-MVP-5001942

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